Electronic computer devices are generally enclosed in a metallic housing called a chassis. The metallic housing prevents electromagnetic interference from either entering or leaving the device. It also provides for the physical structure for the device. The electronic circuitry found within is often composed of integrated circuit chips such as a CPU, placed on a printed circuit board, sometimes referred to as a motherboard. This motherboard must be physically fixed to the chassis so that the motherboard does not vibrate and wobble when the electronic computer is being transported, handled, or installed or used. In addition, this motherboard must have adequate support so that it does not bow or warp in places. Lastly, the motherboard must not be allowed to unintentionally form electrical contact with the grounded chassis of the device. Therefore, devices called stand-off units, sometimes referred to as stanchions or standards, are used to mount the printed circuit board on the chassis while maintaining a predetermined distance of separation between the printed circuit board and the chassis.
The prior art contains numerous designs for stand-off units. FIG. 1 discloses a earlier stand-off unit. Nuts or lugs are integrally formed with the chassis, requiring that motherboards installed in the chassis of FIG. 1 must use all of the lugs 20 to prevent unwanted and unintentional shorting. Thus, a new chassis with a new lug arrangement had to be created each time a new motherboard containing a slightly different through hole arrangement was employed. U.S. Pat. No. 3,066,367 for a Panel Mounting Fastener to German discloses another earlier design for a stand-off unit. Fastening clips mounted on the base of the chassis and positioned around the circuit board allow for a variety of printed circuit boards to be installed in the same chassis. However, one drawback is that Garman's design is inadequate if the motherboard should be large, as there is no support for the motherboard in the center, allowing the motherboard to sag or warp downward. A more sophisticated design to alleviate the above problem can be found in U.S. Pat. No. 4,604,776 for a Spacer For Mounting Boards to Takahashi. Takahashi shows a unit that is easy to install and remove, and can be installed in the middle as well as near the edge of the motherboard. However, Takahashi is just a spacer, as it fails to secure the motherboard to the chassis, thus failing to prevent the motherboard inside the chassis from shaking and vibrating.
U.S. Pat. No. 5,345,366 for a Substrate to Substrate Standoff Assembly to Cheng et al. discloses an interconnect and standoff assembly that provides for electrical coupling between the chassis and the motherboard. In addition, a screw is inserted into a hole formed in the motherboard to attach the stand-off unit to the motherboard. Cheng requires many holes to be formed for each stand-off unit inserted, thus increasing machining costs. Also, Cheng's assembly is made up of more than one part, thus complicating the machining and the assembly of the standoff unit.
Finally, U.S. Pat. No 4,470,178 for a Fastener to Matsui, U.S. Pat. No. 5,191,513 for a Securing Device to Sugiura et al, and U.S. Pat. No. 4,495,380 for a Combined Metal And Plastic Standoff to Ryan et al. each disclose resilient standoff units used to fasten a motherboard to a chassis at a predetermined distance. The drawback with each of these devices is that each are composed of numerous parts, which are difficult to manufacture and assemble.
What is needed is a design for a stand-off unit that is easy to manufacture, that can easily be attached to a detached from a hole in a computer chassis, and that firmly supports and attaches a variety of printed circuit boards of all sizes, including large sizes, to computer chassis.